This invention relates to a method of recovering fat soluble compounds, including but not restricted to pigments such as beta-carotene, from solutions, including but not restricted to those solutions containing microalgal cells.
Intensive cultivation of microalgal cells is widely used as the source of a range of biological materials produced by algae including lipids, pigments and protein. A major limitation to the commercial feasibility of manufacturing such materials using algal biotechnology is the fact that microalgal cells exist at relatively low concentrations in water, are of very small size and can be mechanically and osmotically fragile. The harvesting of algal cells and their products at a commercial scale requires processes which concentrate the small algal cells and their constituent chemical products in an efficient manner which is simple, reliable and requires minimal energy inputs.
To date, methods which have been developed involve using either energy requiring processes such as centrifugation and drying, or use low energy processes such as flocculation, settling or algal behavioural responses which are unreliable and inefficient. Other methods require the disintegration of the algal cells which can render any cellular components useless; for example, degradation of valuable components, such as the carotenoids, via oxidation can occur.
One example of a method which may be used to obtain certain cellular components of algal cells, without any adverse degradation of those cellular components, is described in the patent specification relating to PCT/AU82/00165 entitled xe2x80x9cMethod for Harvesting Algaexe2x80x9d. This specification concentrates on methods for harvesting and concentrating algae, including Dunaliella, from suspensions of a certain salinity, whereby the whole algal cells are adsorbed onto an appropriate adsorbent media The principle finding relating to this invention is that algal cell membranes become hydrophobic at salt concentrations above 3M enabling them to adsorb onto substances having a hydrophobic surface. A number of suitable hydrophobic adsorbents are described in this specification. In addition, a process of rendering certain adsorbents hydrophobic, or more hydrophobic, by treatment with silanes for example is described.
In PCT/AU82/00165 the whole-cell-adsorbent-media complex is then processed using organic solvents which damage the cell membrane and potentially which allow cellular components, such as beta-carotene, to be released while the cellular debris and insoluble cell components remain adsorbed to the adsorbent media The beta-carotene released into the organic solvent in this invention may contains contaminants such as triterpenoids and other lipids and thus further processing is required to isolate only the beta-carotene.
It is an object of the present invention to provide an improved method of extracting fat-soluble compounds or at least to provide the public with a useful choice.
In one aspect of the present invention there is provided a method of extracting fat-soluble compounds from aqueous solutions including the steps:
providing an aqueous solution in which a fat-soluble compound is present;
providing a bed of crystalline metallic ore particles held in an appropriate vessel;
applying the aqueous solution to the bed of crystalline metallic ore particles substantially near the bottom of the bed at a rate sufficient to form and maintain a fluidised bed of crystalline metallic ore particles;
allowing the fat-soluble compound to attach to the crystalline metallic ore particles to form a crystalline-metallic-ore-fat-soluble-compound complex;
providing a wash solution;
contacting the wash solution with the crystalline-metailic-ore-fat-soluble-compound complex to desorb the fat-soluble compound from the complex;
collecting the wash solution containing the fat-soluble compound; and
isolating the fat-soluble compound from the wash solution.
Preferably the crystalline metallic ore particles are magnetite particles.
Preferably the wash solution is contacted with the crystalline-metallic-ore-fat-soluble-compound complex by applying the wash solution to the fluidised bed of crystalline metallic ore particles substantially near the bottom of the fluidised bed and at a rate sufficient to maintain the bed in a fluidised state and the resultant wash solution containing the fat-soluble compound is collected from near the top of, or above, the fluidised bed of crystalline metallic ore particles.
Preferably the method further includes the step of collecting the crystalline-metallic-ore-fat-soluble-compound complex prior to providing a wash solution and contacting the wash solution with the crystalline-metallic-ore-fat-soluble-compound complex.
Preferably the crystalline-metallic-ore-fat-soluble-compound complex is collected from a region substantially near the top of the fluidised bed of crystalline metallic ore particles by means of continuous decantation.
Preferably the crystalline-metallic-ore-fat-soluble-compound complex is dried and stored for a period prior to being contacted with the wash solution.
Preferably the fat-soluble compound is present in the aqueous solution within a number of cells and the aqueous solution is a culture media.
Preferably the cells are those of Dunaliella salina. 
Preferably the fat-soluble compound is a natural pigment.
Preferably the pigment is a carotenoid.
Preferably the carotenoid is beta-carotene.
Preferably the wash solution is an organic solvent.
Preferably the fat-soluble compound is isolated from the wash solution by evaporation or drying.
In another aspect of the present invention there is provided a substantially pure fat-soluble compound obtained using the method of any one of claims 1 to 13.
In yet another aspect of the present invention there is provided a crystalline-metallic-ore-fat-soluble-compound complex obtained using a method as herein described.